Int. J. Chem. Sci.: 14(4), 2016, 2433-2438
ISSN 0972-768X
www.sadgurupublications.com
INVESTIGATIONS ON CLHA AND DOPED CLHA
NANOPOWDERS BY MECHANOCHEMICAL SYNTHESIS
K. RAVINDRANADHa and M. C. RAOb*
a
Physics Division, Department of Basic Sciences & Humanities, Chirala Engineering College,
CHIRALA – 523157 (A.P.) INDIA
b
Department of Physics, Andhra Loyola College, VIJAYAWADA – 520008 (A.P.) INDIA
ABSTRACT
Semiconductor nanoparticles hold the potential for making more efficient solar cells. Solid-State
lighting using LEDs and phosphor material to generate white light is the current research focus in the
lighting industry. The present paper describes the investigations of CLHA and different concentrations of
3d-transition metal ions (Mn2+, Fe3+, Co2+ and Cu2+) doped CLHA nanopowders were prepared by
mechanochemical synthesis. In the case of undoped CLHA nanopowder crystallite size is about 16.15 nm,
while doping with transition metal ions crystallite size decreases and then increases with increasing dopant
concentration. CLHA nanopowders exhibit white emission with the increase of dopant concentration and
are useful for W-LEDs and PDPs.
Key words: CLHA nanopowders, Mechanochemical synthesis, PL and Crystallite size.
INTRODUCTION
The emergent field of nanophotonics deals more particularly with the interaction of
optical fields with matter at nano regime. It creates a technological impact, which perhaps
cannot match up to any other technological developments that have taken place till date as it
deals with every aspect of human life that ranges from building novel materials to medicine.
Nanoparticulate thin films possessing desirable electronic properties are of great interest in
microelectronics. The uniqueness of nanomaterials lies in its large surface to volume ratio,
since nearly all the atoms occupy surface positions. The dependence of specific properties of
clusters on their geometrical dimension is termed as quantum size effect and this effect
originates from two interrelated causes. As the reduction of grain size to nanometerdimensions provides increased strength and hardness, super tough and super strong ceramics
can be synthesized1. These super ceramics can be used in various applications of engineering
such as in aerospace and automotive components and high efficiency gas turbines.
________________________________________
*
Author for correspondence; E-mail: [email protected]
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K. Ravindranadh and M. C. Rao: Investigations on CLHA and….
Semiconductor nanoparticles hold the potential for making more efficient solar cells.
Solid-State Lighting using LEDs and phosphor material to generate white light is the current
research focus in the lighting industry. White LEDs (W-LEDs) will offer high luminous
efficiency, energy savings, environment-friendliness, small volume and long persistence
compared to conventional incandescent bulbs and fluorescent lamps. Phosphors are the
materials, which convert absorbed energy into visible light without going to high temperatures,
i.e. incandescence. Rare earth, transition metal ions which usually correspond to electronic
transitions within the incomplete 4f and 3d shell stimulate luminescence in phosphors
resulting in narrow band spectra.
Usually, phosphors are in the form of crystalline powder with size ranging between
1-100 μm. In order to get high photoluminescence (PL) in nanophosphor particles, large
amount of exciting energy should be absorbed by the activator and simultaneously the
exciton return to the ground state by radiative process. Methods for improving efficiency of
phosphor materials have centred on improving their physical properties by controlling
surface morphology, size of phosphor materials and reducing concentration quenching etc.
Phosphates are compounds that contain oxyanions of phosphorus (V), ranging from the
simple orthophosphate group to condensed chain, ring and network anions. Phosphate
structures are generally rigid, resistant to chemical attack, insoluble and thermally stable.
This leads to some applications as nuclear waste immobilization hosts or negative thermal
expansion materials.
Phosphor layers provide most of the light produced by fluorescent lamps and are
also used to improve the balance of light produced by metal halide lamps. Phosphor
thermometry is a temperature measurement approach that uses the temperature dependence
of certain phosphors for this purpose. The use of labelling or staining agents has greatly
assisted the study of complex biological interactions in the field of biology. In particular,
fluorescent labelling of biomolecules has been demonstrated as an indispensable tool in
many biological studies. The emission of light by a substance not under heat is called
luminescence. Chemical reactions, electrical energy, subatomic transitions and crystal stress
are some of the causes for this behavior. PL is a process in which a substance absorbs
photons and then re-radiates photons. An excitation to a higher energy state and then return
to lower energy state accompanied by the emission of a photon is described by quantum
mechanics. In emissive displays, all colors are obtained by mixing the three primary colors
of red, green and blue at appropriate ratios. The chromaticity of a color can be indicated in
color space which is defined according to the convention of the International Commission on
Illumination (CIE) in a normalized two-dimensional coordinate system2.
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Int. J. Chem. Sci.: 14(4), 2016
Hydroxyapatite (HA) is a calcium phosphate bioceramic that belongs to the family
of apatites. The apatite family is formed a number of elements characterized by having
similar crystallographic structures but not necessarily identical compositions. HA has a
specific composition, Ca10(PO4)6(OH)2, Ca/P ratio of 1.67 and its crystal structure is
hexagonal with a space group P63/m (a = b = 0.943 nm, c = 0.688 nm)3. The apatite structure
is composed of isolated TO4 tetrahedra. Phosphor materials are prepared by several methods
such as high temperature solid-state reaction, mechanochemical, sol-gel, hydrothermal, coprecipitation and emulsion/microemulsion methods. Among these, mechanochemical is an
efficient and cost effective method. The chemical processes occurring during mechanical
action on solids are more specific and versatile. This method has an advantage for the
perturbation of surface-bonded species by pressure to enhance thermodynamic and kinetic
reactions. Rao et al. have published their results on different oxide materials, luminescent
materials, polymers, glasses and on different drugs in their earlier studies4-13.
EXPERIMENTAL
The present paper describes the investigations of CLHA and different concentrations
of 3d-transition metal ions (Mn2+, Fe3+, Co2+ and Cu2+) doped CLHA nanopowders were
prepared by mechanochemical synthesis. The structural and surface morphology were
carried out by using powder XRD, SEM and TEM techniques. The prepared samples are
also characterized by several spectroscopic techniques like Optical absorption, EPR, PL and
FT-IR studies.
RESULTS AND DISCUSSION
In the case of undoped CLHA nanopowder crystallite size is about 16.15 nm, while
doping with transition metal ions crystallite size decreases and then increases with
increasing dopant concentration. At low doping level strain value is large, for that the
crystallite size is small. As the dopant concentration increases from 0.01 to 0.05 mol %, the
strain values are gradually decreases, hence crystallite size is increased. A small shift is
observed in XRD peaks due to the incorporation of transition metal ions into host lattice. In
the present study, decrease in dislocation density is observed with increasing transition metal
ions concentration accompanied to exponential increase in peak intensity. This is evidence
for well crystalline nature of the material. Variation in crystallite size and strain with
respective transition metal ions for (a) undoped & 0.01 mol %, (b) 0.03 mol % and (c) 0.05
mol %, respectively is shown in Fig. 1.
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K. Ravindranadh and M. C. Rao: Investigations on CLHA and….
Fig. 1: Variation in crystallite size and strain with transition metal ions
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Int. J. Chem. Sci.: 14(4), 2016
The morphology of prepared samples exhibit stones/sphere like structures indicates
that each of them is composed of agglomerates with irregular shape and dimension
distributions. It can be seen that by increasing the concentration of transition metal ions, the
degree of agglomeration of prepared samples increased. EDS spectra confirms the presence
of Ca, P, O and transition metal ions in the prepared phosphor materials. TEM
measurements also confirmed the nanocrystalline nature of prepared samples.
From PL data of all prepared CLHA nanopowders, the chromaticity coordinates are
calculated and plotted in chromaticity diagram as shown in Fig. 2. Undoped CLHA
nanopowder is located in blue-green region, Fe3+ and Cu2+ doped CLHA nanopowders are
located in blue region. In the case of Mn2+ doped CLHA nanopowders, emitted color is
shifted from yellow to red region as the dopant concentration increases from 0.01 to 0.05
mol % and it may used in lamps and display devices. Co2+ doped CLHA nanopowders
exhibit white emission with the increase of dopant concentration and is useful for W-LEDs,
PDPs.
Fig. 2: Chromaticity diagram of undoped and transition metal ions doped CLHA
nanopowders
CONCLUSION
The present paper describes undoped and transition metal ions doped CLHA
nanopowders by using mechanochemical method and are characterized by different
spectroscopic techniques. In the case of undoped CLHA nanopowder crystallite size is about
16.15 nm, while doping with transition metal ions crystallite size decreases and then
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K. Ravindranadh and M. C. Rao: Investigations on CLHA and….
increases with increasing dopant concentration. TEM measurements also confirmed the
nanocrystalline nature of prepared samples. From PL data of all prepared CLHA
nanopowders, the chromaticity coordinates are calculated and plotted in chromaticity
diagram. CLHA nanopowders exhibit white emission with the increase of dopant
concentration and are useful for W-LEDs and PDPs.
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Accepted : 23.09.2016